The gas planet is famous for a massive red splotch that we can see from space, the Great Red Spot.

It is a massive anticyclone (the opposite of cyclone) the size of Earth. But lately it’s been shrinking, according to the boffins at NASA. And no one’s quite sure why.

Jupiter’s signature Great Red Spot is on a cosmic diet, shrinking rapidly before our eyes. Here it is in 1995, 2009 and now 2014. Picture: APSource:AP

As a matter of fact, the spot is at its smallest size ever recorded. In the late 1800s the red spot was an oval 41,000km wide. Now it’s a circle that’s 16 500km across. And it is shrinking at a rate of 933km a year.

One possible explanation for the spot’s red colour is that the storm is so powerful it dredges material from beneath Jupiter’s cloud tops and lifts it to higher altitudes. Picture: APSource:AP

Michael Wong, a scientist at the University of California, Berkeley, said the spot is a mystery. Astronomers don’t know why it’s red or shrinking, or what will happen next.

If this pace continues, in 17 years the spot could be gone. Or it could stop at a smaller size.

Wong said one theory is the spot eats smaller storms, and that it is consuming fewer of them.

Whatever it is, it’s quite pretty to look at.

You can see here just how big the Great Red Spot. That’s Ganymede, Jupiter’s moon, lingering in the background. In this Hubble Telescope image, it looks as if Ganymede could fit inside the storm a couple of times. Picture: NASASource:Supplied